GB2436784A

GB2436784A - Kitchen appliance motor controller

Info

Publication number: GB2436784A
Application number: GB0606814A
Authority: GB
Inventors: Kwok Kuen Tse; Kam-Shing Mok
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2006-04-05
Filing date: 2006-04-05
Publication date: 2007-10-10
Also published as: GB0606814D0

Abstract

A kitchen appliance 10 comprises a housing 12, an electric motor 16 housed within the housing 12, a rotatable element 20 mounted or mountable on or in the housing 12 and drivable by the motor 16, and an adaptive controller 22 for automatically controlling the motor 16 based on resistance encountered by the rotatable element 20 through foodstuff being treated by the appliance 10. The controller 22 includes means 24 to 32 for monitoring current being supplied to the in use motor 16, and means 34, 36 for automatically hailing the current once the current reaches a constant or substantially constant magnitude for a predetermined period. The controller prevents the appliance from either running longer than is required or stopping too early when mixing, slicing, dicing and blending food.

Description

2436784

1

KITCHEN APPLIANCE MOTOR CONTROLLER

The present invention relates to a kitchen appliance, particularly, but not exclusively, a blender, having an electric motor and an adaptive controller for 5 automatically controlling the motor.

When mixing, slicing, dicing, and blending food, it is often not apparent to a user when the process has been adequately completed. The user will therefore either often run the appliance for considerably longer than is required, or stop too early in the 10 process, thus resulting in unsatisfactory results.

In the event that the user operates the appliance for too long, electricity is wasted, and the throughput achievable by the appliance is reduced.

15 The present invention seeks to provide a solution to these problems.

According to a first aspect of the present invention, there is provided a kitchen appliance comprising a housing, an electric motor housed within the housing, a rotatable element mounted or mountable on or in the housing and drivable by the motor, 20 and an adaptive controller for automatically controlling the motor based on resistance encountered by the rotatable element through foodstuff being treated by the appliance, the controller including means for monitoring current being supplied to the in use motor, and means for automatically halting the current once the current reaches a constant or substantially constant magnitude for a predetermined period.

2

Preferable and/or optional features of the invention are set forth in claims 2 to 8, inclusive.

According to a second aspect of the invention, there is provided an adaptive 5 controller for automatically controlling an electric motor of a kitchen appliance based on resistance encountered by the motor through foodstuff being treated by the appliance, the controller comprising means for monitoring current being supplied to the in use electric motor of the appliance, and means for automatically halting the current once the current reaches a constant or substantially constant magnitude for a 10 predetermined period.

The present invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which :

Figure 1 is a side view of a first embodiment of a kitchen blender, in accordance 15 with the present invention;

Figure 2 is a generalised circuit diagram of an electric motor and an adaptive controller of the blender;

Figure 3 is a graph showing typical oscillation of rms value of current over an initial period when the motor is first energised;

20 Figure 4 is a graph showing a pulse signal derived from the current-time waveform of Figure 3, and a control signal supplied to a switch of the controller; and

Figure 5 is a generalised circuit diagram of a digital adaptive controller of a second embodiment of the blender, in accordance with the present invention.

3

Referring firstly to Figures 1 to 4 of the drawings, there is shown a first embodiment of a blender 10 which comprises a housing 12 forming a base, and an openable and closeable container 14 which is demountably attached to the housing 12.

5 An electric motor 16, connectable to a mains AC electrical power source 18, is provided in the housing 12, and a rotatable blending element 20 for cutting foodstuff is provided within the container 14. The blending element 20 is rotatably drivable by the electric motor 16, when the container 14 is engaged with the housing 12. The housing 12 includes a user interface for manually switching the electric motor 16 ON and OFF,

10 thereby manually controlling the blender 10.

An adaptive controller 22 is also provided in the housing 12, electrically connected in series with the motor 16. A flywheel diode 23, connected in parallel with the motor 16, can be utilised to protect the controller 22 in high-power applications.

15

The controller 22 includes means for monitoring current being supplied to the motor 16, and means for automatically halting the current once the current reaches a constant or substantially constant magnitude for a predetermined period.

20 The current monitoring means includes a current sensor 24, and a series network connected to the sensor 24. By way of example, the current sensor 24 can be a resistor connected to neutral, a voltage-drop resistor, a transformer / toroidal coil type current sensor, or a Hall effect type current sensor. The voltage-drop resistor, in particular, is convenient, since it is both simple and cost-effective.

4

The series network includes a diode 26, a low-pass filter (LPF) 28, a DC blocker 30, and a comparator 32 for outputting a pulse signal T corresponding to current being supplied to the motor 16.

5 Typically, the neutral of the AC circuit is earth. In the case of a DC supply, the neutral represents the negative leg of the circuit.

The current halting means includes a switch 34, which can be a Triac and which is typically closed, and means for controlling the switch 34 based on the pulse signal T 10 outputted by the comparator 32 of the current monitoring means. In this case, the switch controlling means includes a time-delay monostable vibrator 36 connected in series with the comparator 32 of the current monitoring means.

With reference to Figures 3 and 4, once the blender 10 is connected to the mains 15 power source 18 and a user has utilised the user interface on the housing 12 to energise the motor 16 and begin the blending process, current is supplied to the motor 16, and a graph similar to that shown in Figure 3 can be typically plotted. For an initial period To, the current supplied oscillates due to the load on the motor 16. The load varies depending, at least in part, on the resistance imparted by the foodstuff on the blending 20 element 20, which is being driven, either directly or indirectly, by the motor 16. For example, blending coconut will typically impart higher resistance than blending pear. However, over time To, the amplitude of the oscillations decrease, and the magnitude of the current reaches a constant or substantially constant value.

5

The current being fed to the motor 16 is passed through the current monitoring means of the controller 22. The peak amplitude of the current signal is extracted by being passed through the low-pass filter 28 and the DC blocker 30 to remove the mains frequency and the DC offset. Peak amplitude signal V/ is then compared with a 5 reference voltage signal Vref by the comparator 32, and a square-wave pulse signal T is outputted to the time-delay monostable vibrator 36 of the current halting means.

At the monostable vibrator 36, when a pulse of the pulse signal T is not detected for a predetermined time period, in other words, when a time period tn between pulses

10 becomes equal to or greater than a predetermined period T, it is determined that the current has reached a constant or substantially constant value. The blending process is thus complete, and a control signal Q, being output by the time-delay monostable vibrator 36 to the switch 34, goes HIGH, causing the switch 34 to open and automatically deenergising the motor 16.

15

Although not shown, the opening of the switch 34 causes the mains power to the user interface to be halted, so that, when the control signal of the monostable vibrator returns to LOW, the blending process does not automatically restart.

20 Typically, in more advanced appliances, more sophisticated features of operation, protection and the user's interface are usually controlled by an embedded electronic system, such as circuitry incorporating a microcontroller unit (MCU). As shown in Fig. 5, an adaptive controller 122 of a second embodiment of the blender can utilise a algorithmic digital processing to continuously sample a discrete amplitude In of

6

the current / and to analyse the difference between a present value and previous values. For example, current sensor 124 of current monitoring means outputs a signal to an analogue-to-digital controller (ADC) 140, via diode 126, for sampling. Providing a present sampled current signal /„ outputted from ADC 140 is greater than 0, then the 5 present sampled current signal I„ is compared to a previous sampled current signal /„_/. If /„ is equal to or within a predetermined acceptable tolerance of I„.j over a predetermined time period, it is determined that the current has reached a constant or substantially constant value. A blending process is thus complete, and a control signal Q' is outputted, causing switch 134 to open, thus automatically deenergising the motor.

10

Although not shown, the accuracy of the above analysis can be further improved by using digital filtering techniques, such as taking an average 1„. It is straightforward to realize the above monitoring means and control means in an embedded system.

15 The adaptive controllers can be applied to any electrically operable domestic appliances, such as electric whisks and mixers, having a housing, an electric motor in the housing, and a rotatable element which is drivable by the motor and which, in use, has a resistive force imparted to it by contact with foodstuff.

20 The person skilled in this field will realise that the current monitoring means and/or the current halting means can, additionally or alternatively, include one or more components which differ from those described above in order to achieve the same or a comparable result.

7

It is thus possible to provide an electrically operable domestic appliance having an adaptive controller which automatically controls an electric motor of the appliance based on resistance imparted by foodstuff being treated. A uniform or substantially uniform level of treatment is thus ensured. Consumption of electricity and time spent 5 utilising the appliance are also optimised.

The controller of the first embodiment is cost effective to produce, since it does not require expensive integrated circuits and sensors. The controllers are simple to incorporate into existing appliances, without requiring modification of the existing user 10 interface.

The embodiments described above are given by way of examples only, and various other modifications will be apparent to persons skilled in the art without departing from the scope of the invention, as defined by the appended claims.

15

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Claims

1. A kitchen appliance comprising a housing, an electric motor housed within the housing, a rotatable element mounted or mountable on or in the housing and drivable by the motor, and an adaptive controller for automatically controlling the motor based on resistance encountered by the rotatable element through foodstuff being treated by the appliance, the controller including means for monitoring current being supplied to the in use motor, and means for automatically halting the current once the current reaches a constant or substantially constant magnitude for a predetermined period.

2. A kitchen appliance as claimed in claim 1, wherein the monitoring means includes means for generating an output signal, and the current halting means includes a switch and means for controlling the switch based on the output signal.

3. A kitchen appliance as claimed in claim 2, wherein the monitoring means includes a current sensor, and a series network including a diode, a low-pass filter, a DC blocker, and a comparator, the in use comparator comparing an input signal with a reference signal to obtain the output signal.

4. A kitchen appliance as claimed in claim 2 or claim 3, wherein the output signal is a pulse signal and the switch controlling means controls the switch to halt the current to the motor when a period between pulses of the pulse signal is equal to or greater than a predetermined value.

5. A kitchen appliance as claimed in claim 4, wherein the switch controlling means of the current halting means includes a time-delay monostable vibrator which

9

controls the switch to halt the current when the said predetermined value is reached and/or exceeded.

6. A kitchen appliance as claimed in Claim 2, wherein the switch controlling means and the monitoring means form part of an embedded electronic system of

5 the appliance, and the monitoring means further includes: a current sensor, a diode, an analogue-to-digital converter, and an algorithm which analyses discrete amplitudes of current to generate the output signal.

7. A kitchen appliance as claimed in any one of the preceding claims, wherein the controller is electrically connected in series with the motor.

10 8. A kitchen appliance as claimed in any one of the preceding claims, wherein the appliance is a blender.

9. An adaptive controller for automatically controlling an electric motor of a kitchen appliance based on resistance encountered by the motor through foodstuff being treated by the appliance, the controller comprising means for

15 monitoring current being supplied to the in use electric motor of the appliance,

and means for automatically halting the current once the current reaches a constant or substantially constant magnitude for a predetermined period.

10. A kitchen appliance, substantially as herein before described with reference to the accompanying drawings.

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